ch70 - CHAPTER 7: FLOW PAST IMMERSED BODIES *(unbounded...

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CHAPTER 7: FLOW PAST IMMERSED BODIES *(unbounded flows)
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Ch 7: FLOW PAST IMMERSED BODIES FLAT PLATE (CAN’T HAVE FULLY DEVELOPED FLOW) What is wrong with this picture?
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BLUNT OBJECT Ch 7: FLOW PAST IMMERSED BODIES (CAN’T HAVE FULLY DEVELOPED FLOW)
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Paradoxes Pipe Flow - hydraulic engineers knew Δ p ~ U avg 2 - theory and capillary tube showed Δ p ~ U avg - several other paradoxes for external flows as well Drag - theory predict no drag (1744 –d’Alembert)
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Shape and Flow – Irvin Shapiro http://web.mit.edu/fluids/www/Shapiro/ncfmf.html Fluid Dynamics of drag Parts I - IV
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Air speeds up to 230 mph, drag forces object in jet upwards, causing spring to extend downwards Pressurized settling chamber underneath desk EXPERIMENTAL SET UP
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Tubing leads air from settling chamber to U-tube manometer which is calibrated in mph, so can measure drag force and speed. Can measure U and Drag
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Question #1: sketch the graph of drag on smooth 3” diameter sphere vs velocity PARADOX #1 SPHERE 0 250 MPH 125 MPH
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D ~ U 2 D ~ U D = 6 πμ RU Drag lower at higher speed! 250 mph 125 mph SPHERE
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D ~ U 2 D ~ U D = 6 πμ RU ASIDE: viscous drag at low Re number does not depend on density or pressure. SPHERE ASIDE
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“The new law that he {Maxwell ~1862} predicted seemed to defy common sense. It was that the viscosity of a gas – the internal friction that causes drag on a body that moves through it – is independent of pressure. One might expect that a more compressed gas to exert a greater drag.” The Man Who Changed Everything – Basil Mahon Turns out that the effect of being surrounded by more molecules is exactly cancelled out by the fact that their mean free path is less.
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When very small dust particles fall through one column of air at 1 atmospheric, they fall at the same terminal velocity as if it was 0.01 atmosphere.
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is roughened, what happens to drag? PARADOX #2
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This note was uploaded on 04/26/2010 for the course MAE 101B 101B taught by Professor Rohr during the Summer '09 term at UCSD.

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ch70 - CHAPTER 7: FLOW PAST IMMERSED BODIES *(unbounded...

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